How do you sort the keys in HashMap?

Problem statement:
Write the java code to sort the keys in HashMap.

1. import java.util.HashMap;
2. import java.util.Set;
3. import java.util.TreeSet;
4. public class Test {
5. public static void main(String[] args) {
6. HashMap<String, String> m = new HashMap<String, String>();
7. m.put("key45", "aa");
8. m.put("key12", "zz");
9. m.put("key39", "cc");
10. m.put("key27", "bb");
11. Set<String> s = m.keySet();
12. s = new TreeSet<String>(s);
13. System.out.println(s);
14. }
15. }

Output:
[key12, key27, key39, key45]